The manufacture of cellulosic insulation in accordance with the present state of the art begins with a grinding operation in which newspapers are shredded to provide a mass of cellulosic fibers.
A fire retardant composition is then mixed with the cellulosic fibers in order to coat them with the fire retardant material. This mixing is conventionally accomplished in one of two manners.
The fire retardant may be dissolved in a suitable solvent such as water and then sprayed into a stirred mass of the shredded cellulosic material. The spray application of the retardant may be performed simultaneously with a grinding step for shredding the cellulosic material or as a subsequent step.
One of the major disadvantages of the solution spray application system is that the resultant mixture becomes a sticky, gummy mess which is difficult to handle and requires drying.
A different method for using water in the manufacture of cellulosic insulation includes applying water to the particles of cellulosic material which carry fire retardant powder particles on their surfaces. The water forms a solution of the fire retardant composition on the cellulose fibers. This method is limited to non-hygroscopic, boric acid or borate fire retardant compositions. The amount of water required to obtain acceptable chemical distribution is approximately 30% of the weight of the shredded cellulose fibers. This requires prolonged treatment under hot and humid conditions, and requires a drying treatment to lower the moisture content of the final product to a practical level. Additionally, the water applied to the fire retardant and fiber mixture does not change the chemical composition of the fire retardant agent. The water added is for the purpose of improving distribution of the fire retardant agent on the fibers.
Alternatively fire retardant may be applied in dry powdered form which may be mixed with stirred cellulosic fibers during a grinding operation or an independent stirring operation. However, difficulty is experienced in effecting the adhesion of the fire retardant particles to the cellulosic shredded material with a sufficiently durable bond. It also has been difficult or impossible to obtain a complete and uniform coating of fire retardant on the cellulosic particles.
These latter problems have, in the current state of the art, been reduced somewhat by spraying small quantities of water on the cellulosic material before mixing in the fire retardant in order that the dry fire retardant particles will be wetted when they come into random contact with the cellulosic fibers. Thus, the particles are adhered to the cellulosic fibers by the wetting activity of the moisture.
However, even this system has several disadvantages including the still somewhat agglomerated or clumpy nature of the finished product, the non-uniform and incomplete coating of the fibers and the need for drying the insulation after the retardant is applied.
While attempting to find a means for reducing the dust generated during the manufacture of shredded cellulosic insulation, an anti-static agent was sprayed upon the shredded cellulosic insulation. It was eventually discovered that advantages could be gained by mixing and effecting the adhesion of an anti-static agent with the fire retardant agent prior to depositing the fire retardant agent on the shredded cellulosic material. This discovery was the subject of my prior patent U.S. Pat. No. 4,645,696. After the anti-static and the fire retardant agent were mixed, they are mixed with and deposited upon the shredded cellulosic material.
The anti-static agent may be added, mixed or blended with a particulate fire retardant agent either by mixing or spraying a liquid solution of the anti-static agent onto the particulate fire retardant agent or by blending a particulate anti-static agent with the particulate fire retardant agent.
Preferably the shredded cellulosic material is substantially unwetted at the time it is mixed with a mixture of anti-static agent and fire retardant agent. It has been found that the dry shredded cellulosic material accomplishes better coating of the cellulosic fibers with the fire retardant agent than is accomplished if the cellulosic fibers are prewetted as done in the prior art.
In my U.S. Pat. No. 4,645,696 the anti-static constituent of the mixture of anti-static agent and the retardant agent was preferably on the order of 0.1% to 1% by weight in a system in which the finished product is loaded with 20% retardant. The important proportion is believed to be the proportion of anti-static agent used in the finished insulation product. Preferably, in the invention of the prior patent, the finished product was 0.02% to 0.2% by weight of anti-static agent.